2-bbl on 301 running WAY too lean, but why/how to fix?

All,

Ugh, ok, I hope I'm not breaking any sort of quasi-cross-posting rules, and will beg/grovel for forgiveness if I have, but I'm in a bit of a pickle.

Made a post about fuel delivery issues in my Anti-Project thread... and am at a loss. Though I admit that, for the most part, carburetors are a little bit of a black box for me. I mean, I understand the basics, but not why some things may or may not be happening.

In any case, I can't get the car to idle. I think the previous owner(s), or a mechanic of one of the previous owners, "solved" a problem by increasing the idle speed. The symptom is as I describe in the other thread - it'll only idle, even when warmed up, if I hold the choke plate about 3/4 closed - then it idles fast, and quite smooth.

Otherwise, fuel dribbling in venturis (though still too lean despite that), very irregular running, and generally will conk out. I've replaced leaking fuel hoses, and the fuel filter. I do not THINK I have any vacuum leak issues, but don't really know for sure. I don't hear anything untoward, but my Mark I ear isn't exactly all it's cracked up to be.

Any advice/assistance/known-good-dualjets-avalable-to-borrow/etc. on how to proceed?

I came across a reference (AFTER posting this thread, of course) that says that, if there's fuel dribbling, then the idle is set too high, and it's not running on the idle circuit. Does that sound at all accurate?

That said, I also wondered about the fuel pump, if I was getting steady enough pressure from it, etc. Ugh, wasn't looking at putting real money into this thing - but a carb rebuild/replacement (ok, I know I was able to get a 2-bbl carb on a 318 rebuilt, I provided the kit, by a really old-school mechanic for $70, but that was in the early 90s!)

Ah well - check (or replace) fuel pump, check and make sure nobody did a hasty re-working of vacuum lines... and if my denial and desperate attempt to avoid changing the carb doesn't yield results... then a carb it shall have to be.

EDIT: Anyone ever dealt with these guys? How are their carbs? Came across them on a really hasty search for carburetors... http://www.nationalcarburetors.com/lookup.aspx?partnum=nd2875

EDIT2:

seawolf18 said:

You could try and find a 4 bbl manifold for it and put a small 4bbl carb on it. I don't remember if edelbrock makes a manifold for it.

Click to expand...

Hmm . . I was unaware that ANYONE made aftermarket intakes for the 301. Of course, until a few months ago, all I knew about the 301 was as an interesting emissions/economy era footnote from the 70s.

I am an idiot.

There. I said it. I. Am. An. Idiot. 😳

Oh, I don't hear any vacuum leaks. Oh, the hoses look good. Oh, it's probably something other than that. Blah Blah Blah.

Well, I was tinkering with it today. And I went under the hood. And I saw this short, though rather thick, rubber hose near the carb. And there appeared to be a black line or shadow on it.

Uh, no, it wasn't a dark line or discoloration of the hose. It was splitting. So I shoved it down further as a temporary measure.

Notable improvement in the idling of the car. As in, it will pretty much idle now. Not great, but at least I *can* idle.

Though I still may try turboaudi's suggestion, just as a dotting-the-Is-and-crossing-the-Ts sort of step.

VERY belated update to this.....


Alright, so I've got all the 5/32" lines replaced. Vacuum lines are all now routed correctly (there were only one or two mixups before by the previous owner)

Idle is still fairly crappy - the best I can manage is a rough-ish idle with 14-15 inches of vacuum. That's with the idle mixture screws turned out 4-1/2 turns. It's VERY insensitive to idle mixture adjustments.

Idle will still waver in 2-3 second intervals half the time. I hear a slight slurp as a drop of gas drips in the carb, vacuum jumps to 16 and engine speed jumps up with it, then over the course of 2-3 seconds, falls to 13-14. Lather, rinse, repeat. When that's not happening, it's mostly at 14 fairly steadily.

I can get it to smooth out, but that's by adjusting the idle upward and then there's a sudden clearing up, I think at that point the throttle blades are open enough that it's transitioning out of the idle circuit.

Putting the car in gear means playing with the gas pedal to keep it running, otherwise it slows down a lot, sputters, and dies.

There's only TWO things I can think of.

1) Bad idle circuit on the carb (it runs so amazingly when not idling)
2) Bad fuel pump (can a pump be feeble at low speed, but perfect above that?)

I suspect the former. I will likely eventually change the fuel pump anyway (it's the original, after all).

Still, I'd rather be sure before I assume the carb itself is at issue. Anyone nearby have a known good 2-bbl that I can throw on this thing to try out, just to be sure the carb is the source of the trouble?